I have to find the calculation of Van't Hoff factor "i" for NaCl and sucrose. The directions say to use the equation
delta Tf = kf X m X i
and to use Kf for water = -1.86C/m
So I have the molality of NaCl and sucrose as well as delta Tf so for NaCl I plugged the numbers into the equation.
2.5C = -1.86C/m X 0.6697mol/kg X "i"
2.5 = -1.2456 X i
i=-2
Did I do this correctly? Thank you for your help!!
6 answers
If you have the right m, yes.
Is it ok that "i" is negative?
No, i is not negative, ever.
Forget the - sign for 1.86 unless you are going to be consistent and place a - sign for 2.5. Wasn't that 2.5 C BELOW the normal freezing point. That's why I don't worry about the signs. You KNOW m is positive you KNOW Kf is negative, you KNOW delta T is a depression. Usually you go through all this to calculate m and you KNOW molality is +.
Forget the - sign for 1.86 unless you are going to be consistent and place a - sign for 2.5. Wasn't that 2.5 C BELOW the normal freezing point. That's why I don't worry about the signs. You KNOW m is positive you KNOW Kf is negative, you KNOW delta T is a depression. Usually you go through all this to calculate m and you KNOW molality is +.
Ok and for sucrose I did
-4.5C = -1.86C/m X 0.1004 mol X i
-4.5 = -0.1867i
i =24
Can i be a big number like this?
-4.5C = -1.86C/m X 0.1004 mol X i
-4.5 = -0.1867i
i =24
Can i be a big number like this?
Nevermind, I made a mistake im sorry. Disregard the question.
I don't believe 24. i should be 1 for sucrose.
2 answers